1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, particularly, to a color filter substrate for the LCD device and a fabricating method of the color filter substrate wherein the color filter layer of the color filter substrate is made of lyotropic liquid crystal and acts as a polarizer.
2. Discussion of the Related Art
LCD devices are developed as the next generation display devices because of their lightweight, thin profile, and low power consumption characteristics. In general, an LCD device is a non-emissive display device that displays images using a refractive index difference having optical anisotropy properties of liquid crystal material that is interposed between a thin film transistor (TFT) array substrate and a color filter (C/F) substrate. Presently, among the various types of LCD devices commonly used, active matrix LCD (AM-LCD) devices have been developed because of their high resolution and superiority in displaying moving images. The AM-LCD device includes a TFT per each pixel region as a switching device, and first and second electrodes, the second electrode being used as a common electrode.
The LCD device includes upper and lower substrates, and a liquid crystal layer interposed therebetween. The upper substrate and lower substrate are commonly referred to as a color filter substrate and an array substrate, respectively. A common electrode and color filter layers are formed on the upper substrate through processes for fabricating a color filter substrate. Similarly, TFTs and pixel electrodes are formed on the lower substrate through processes for fabricating an array substrate.
A liquid crystal display device according to a related art is explained in detail with reference to FIG. 1 which shows a perspective view of an LCD device according to the related art.
Referring to FIG. 1, upper and lower substrates 10 and 20 are arranged to face each other with a liquid crystal layer 40 interposed therebetween. On an inner surface of the upper substrate 10, a color filter layer 14 and a common electrode 18, which functions as one electrode for applying an electric field to the liquid crystal layer 40, are subsequently formed. The color filter layer 14 includes red, green and blue sub color filters for passing only the light of a specific wavelength, and a black matrix 12 that is disposed in the boundary regions of the sub color filters and shields the light from the regions in which the alignment of the liquid crystal layer 40 is uncontrollable. On an inner surface of the lower substrate 20, a plurality of gate lines 22 and a plurality of data lines 24 are formed in a matrix array. A thin film transistor T, which functions as a switching device, is disposed at a region where each gate line 22 and data line 24 crosses, and a pixel electrode 36 that is connected to a thin film transistor T is disposed at each pixel region P defined by the region where the corresponding gate and data lines 22 and 24 cross.
Although not shown, this LCD panel further includes upper and lower polarizing plates which are placed on the backsides of the upper and lower substrates 10 and 20. A backlight unit which includes a lamp and an optical sheet, and top and bottom cases supporting the LCD panel is placed on the backside of the lower substrate 20.
FIG. 2 is a schematic cross sectional view showing an LCD device having polarizing plates according to a related art.
In FIG. 2, an LCD panel 45 includes an array substrate 21, a color filter substrate 11 facing the array substrate 21, a first polarizing plate 50 on the backside of the array substrate 21 and a second polarizing plate 52 on the backside of the color filter substrate 11. Although not shown, a liquid crystal layer is disposed between the color filter substrate 11 and the array substrate 21
Among them, the array substrate 21 includes a plurality of thin film transistors T shown in FIG. 1 and a plurality of pixel electrodes 36 each connected to the corresponding thin film transistor T. The color filter substrate 11 includes a color filter layer 14 and a common electrode 18. The pixel electrode 36 is practically formed in each pixel region P shown in FIG. 1 in comparison with the common electrode 18.
Generally, the color filter layer 14 includes red, green and blue sub-color filters which are arranged in order. Each of the red, green and blue sub-color filters is located to correspond to each pixel region P as shown in FIG. 1. The color filter layer 14 is manufactured by a pigment dispersion method known to have a good elaborateness and reproducibility.
Hereinafter, a fabricating method of the color filter substrate by the pigment dispersion method will be explained referring to FIGS. 3A-3D. Particularly, FIGS. 3A to 3D are schematic cross sectional views showing a fabricating process by a pigment dispersion method of a color filter substrate for an LCD device according to a related art.
In FIG. 3A, a black matrix 12 is formed by coating (or depositing) a light blocking material such as black resin and chromium (Cr) based materials on a substrate 10. For example, the black matrix 12 may be patterned and manufactured by photolithography using a photoresist pattern. The black matrix 12 is located in the boundaries of the pixel regions P in order to prevent leakage and to shield the thin film transistors T from incident lights as shown in FIG. 1.
In FIG. 3B, a red resist layer 13 is formed by spin coating or bar coating of a red resist material over the entire surface of the substrate 10 including the black matrix 12.
Next, a mask 15 having a transmissive portion TP and a shielding portion SP is disposed over the substrate 10 having the black matrix 12, and then the red resist layer 13 of the substrate 10 is exposed to UV light through the mask 15.
For example, the red resist layer 13 is a negative type material such that an exposed portion of the red resist layer 13 is patterned into a red sub-color filter pattern. Therefore, the transmissive portion TP of the mask 15 corresponds to the portion of the red resist layer 13 that will be patterned into a red sub-color filter during the step of exposing.
In FIG. 3C, the exposed portion of the red resist layer 13 shown in FIG. 3B is patterned into a red sub-color filter 14a by developing the exposed portion of the red resist layer 13. Next, curing the red sub-color filter 14a is performed to cure the red sub-color filter 14a. 
In FIG. 3D, green and blue sub-color filters 14b and 14c are sequentially formed by the same processes as the process of forming the red sub-color filter 14a. The green and blue sub-color filters 14b and 14c are made of green and blue resist materials, respectively. The red, green and blue sub-color filters 14a, 14b and 14c constitute a color filter layer 14.
Next, an overcoat layer 16 is formed on the entire surface of the color filter layer 14 over the substrate 10, and a common electrode 18 is formed using transparent conductive materials including indium tin oxide (ITO), indium zinc oxide (IZO) and indium tin zinc oxide (ITZO) on the overcoat layer 16. The overcoat layer 16 is specifically formed to protect the color filter layer 14 and to compensate for the step height of the color filter layer 14.
As explained above, the color filter substrate according to the related art is manufactured through the multiple steps of coating, exposing, developing and curing the color resist materials. After aligning the manufactured color filter substrate and the array substrate to face to each other, an LCD panel is manufactured by attaching the color filter substrate and the array substrate and by interposing a liquid crystal layer between the color filter substrate and the array substrate. Next, by attaching polarizing plates on the backsides of the color filter substrate and the array substrate, respectively, the LCD panel is completed.
FIG. 4 is a schematic cross sectional view showing the color filter substrate, which is manufactured by the process of FIGS. 3A to 3D and has a polarizing plate.
In FIG. 4, a polarizing plate 52 is placed on the backside of the color filter substrate 11 shown in FIGS. 2 and 3D having the black matrix 12, the color filter layer 14, the overcoat layer 16 and the common electrode 18.
However, the LCD devices according to the related art have a number of problems and limitations. For instance, the polarizing plate 52 for the color filter substrate 11 has a light damage due to an interface reflection. Further, because the thickness range of the polarizing plate 52 is more than 200 micrometers, the use of the polarizing plate 52 interferes significantly with fabricating a light-weight and slim LCD device. Furthermore, the polarizing plate 52 is expensive and the use of such polarizing plates increases the cost of the LCD device. Moreover, the polarizing plate 52 includes a base film, a polarizer layer, and the like. Because the base film is selected from a hard material, the flexibility of the base film is poor. Therefore, it is practically difficult, if not impossible, to use such polarizing plates in flexible displays.